An electricity meter is an electrical energy measurement device that accurately measures the amount of electrical energy flowing to consumers from energy suppliers. The amount of electrical energy measured by the electricity meter is then used to determine the electricity bill for which the energy suppliers should charge.
According to some industrial standards or regional standards, a qualified electricity meter should be capable of providing many working parameters, such as an effective value of the current flowing through power lines, either a phase line or a neutral line, an effective value of the voltage on the phase line, and an energy accumulation produced by the corresponding currents. The voltage on the phase line is referring to a voltage difference between the phase line and a reference potential such as ground or the neutral line. Specially, for electricity meters having anti-tamper function, it is generally required to monitor both the current in the phase line and the current in the neutral line simultaneously. When a big difference between the two currents is detected, the electricity meter could give a warning signal to indicate that the electricity is not properly used.
One approach has been used to simultaneously monitor the currents in the phase line and the neutral line by means of two detection channels, each of which comprises a current detector and an analog to digital converter (ADC). In this approach, the current in the phase line is detected by one detection channel, and the current in the neutral line is detected by the other detection channel. Specifically, the current detector is configured to sample the currents and generate current detection signals of the respective power lines. The A/D converter of each detection channel is configured to convert the current detection signal to a digital signal, which is further provided to a signal processing module. The A/D converters can be sigma-delta converters with high resolution. However, two A/D converters require more chip area, and therefore lead to higher power consumption and cost.